1. Field of the Invention
The present invention relates to a heat exchanger including exchanger tubes equipped with fins which extend transversely of the sides of the tubes. The exchanger tubes have an elongated cross-section in the flow direction of the outer exchanger medium. The exchanger tubes have a length which is several times greater than the width thereof. The exchanger tubes are arranged in a row extending transversely of the flow direction of the outer exchanger medium and the tubes are with the ends thereof attached to tube plates.
2. Description of the Related Art
German patent 34 19 734 discloses a heat exchanger which is capable of exchanging heat, for example, between gases and liquids or between gases and condensing vapors. Such a heat exchanger is used predominantly for cooling air or condensing vapors by means of air.
Steel fins are used especially in connection with exchanger tubes of steel. The steel fins are dip-galvanized. Such fins are punched in appropriate machines from plates or strips, are provided with holes adapted to the cross-section of the exchanger tubes and are subsequently pushed in the longitudinal direction onto the exchanger tubes. The subsequent galvanization by dipping not only has the purpose of protecting the exchanger tubes and the fins, but simultaneously produces the metal-to-metal connection of the exchanger tubes with the fins.
The exchanger tubes which are slender in the flow direction of the outer exchanger medium and are essentially oval, are arranged in at least one row next to each other between two tube plates. The tube ends are attached to the tube plates. In addition to the tube plates, stable support structures are used for connecting the exchanger tubes.
In the above-described exchanger tubes whose cross-section is non-circular, the fins as well as the sides of the tubes connected to the fins are subjected to bending moments which occur, especially when vacuum exists in the exchanger tubes.
If a certain width of the sides of the tubes, for example, approximately 200 mm, is exceeded in such exchanger tubes, and if the fin dimensions and rib spacings are conventional, i.e., having a thickness of approximately 0.35 mm, a height of approximately 15 mm and a spacing of approximately 2.5 mm, and the sides of the tubes have a conventional thickness of about 1.5 mm, it may easily occur that the permissible bending stresses of the thin fins are exceeded and distorsions of the fins are caused as a result. Moreover, the connection between the exchanger tubes and the ribs which is usually effected by zinc may be damaged. This damage results in the significant disadvantage that the flow of heat between the exchanger tubes and the fins is disturbed, without the reason for this problem being visible or apparent.
In manufacturing the known heat exchanger, the machine procedures of punching out the fins and sliding the ribs onto the exchanger tubes must be carried out with high precision, so that it is ensured that the zinc provides as close as possible a connection between the exchanger tubes and the fins. These procedures are very complicated and cumbersome. Since, in addition, the fins are slid over the exchanger tubes, a significant amount of material is cut out of the fins to provide for the cross-section of the exchanger tubes. A large quantity of this material which has ben cut out is inevitably discarded unused as scrap material.
Another property of the known heat exchanger is the fact the heat exchanger tubes are galvanized individually. For this purpose, each exchanger tube must be pressed flat and tightly welded at the ends thereof, so that only the outer surfaces are pickled and passivated and the inner surfaces are not galvanized. This is also cumbersome and complicated. After the exchanger tubes have been galvanized, it is necessary to remove the ends which have been pressed flat and welded. This also requires an additional operation and produces essentially useless waste material.
Subsequently, it is necessary to join the individual exchanger tubes together by means of the support structures already mentioned above in order to obtain the heat exchanger which must be constructed so as to be self-supported over the length thereof.
Accordingly, the manufacture of a heat exchanger of the known type is relatively cumbersome and requires time-consuming work steps. In addition, the manufacture becomes more difficult because of measures required for avoiding damage to the surface protection applied by means of dipping during the assembly of the heat exchanger.
Moreover, due to the inner negative pressure and/or the outer excess pressure, significant forces act on the large-area sides of the slender exchanger tubes. Consequently, when a certain degree of slenderness is exceeded, the sides of the tubes are pressed-in if suitable measures, such as, supports, are not provided. In this connection, an embodiment of the known proposal provides that the sides of the tubes are supported relative to each other by means of at least one internal transverse web.